(57) In a semiconductor laser, a multiple quantum well type active layer consisting of
barrier layers (15,16,17) and active layers of well layers (11), each of which has
a thickness less than the de Broglie wavelength of electons, is doped with an impurity,
and the impurity density is made higher in the barrier layer (15, 16, 17) than in
the well layer (11). Where the multiple quantum well active layer is held between
p-type and n-type cladding layers (14,13), the well layer (11) is undoped, the part
(15) of the barrier layer lying in contact with the well layer (11) is undoped, and
the other part (17) of the barrier layer close to the p-type cladding layer (14) is
put into the n-conductivity type while that (16) of the barrier layer close to the
n-type cladding layer (13) is put into the p-conductivity type.
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